Field of the Invention
The present invention relates to a spin-orbit torque type magnetoresistance effect element, and a method for producing a spin-orbit torque type magnetoresistance effect element. Priority is claimed on Japanese Patent Application No. 2016-210530, filed Oct. 27, 2016, and Japanese Patent Application No. 2017-138384, filed Jul. 14, 2017, the contents of which are incorporated herein by reference.
Description of Related Art
Examples of known magnetoresistance effect elements include giant magnetoresistance (GMR) elements composed of a multilayer film of ferromagnetic layers and non-magnetic layers, and tunnel magnetoresistance (TMR) elements which use insulating layers (tunnel barrier layers, barrier layers) for the non-magnetic layers. Generally, TMR elements have a larger element resistance than GMR elements, but the magnetoresistance (MR) ratio is larger than GMR elements. Consequently, TMR elements are attracting much attention as elements for magnetic sensors, high-frequency components, magnetic heads and non-volatile random access memory (MRAM).
MRAM reads and writes data by utilizing the characteristic that when the relative orientation between the magnetizations of two ferromagnetic layers that sandwich an insulating layer is changed, the element resistance of the TMR element changes. Examples of known methods for writing to MRAM include a method in which a magnetic field generated by an electric current is used to perform writing (magnetization reversal), and a method in which a spin transfer torque (STT) generated by passing an electric current through the stacking direction of a magnetoresistance effect element is used to perform writing (magnetization reversal).
In recent years, there has been a demand for higher integration of MRAM (for example, see Patent Document 1). In order to achieve high-density of integration of MRAM, the TMR elements must be made more compact. However, if the TMR elements are made more compact, the magnetization stability decreases. Decreases in the magnetization stability can cause rewriting of data under the influence of heat or the like (for example, see Patent Document 2). MRAM has the purpose of allowing long-term storage of data, and it is not permissible for the data to be spontaneously overwritten.
As methods for raising the magnetization stability, a method of increasing the volume of the ferromagnetic layers and a method of increasing the magnetic anisotropic energy of the ferromagnetic layers may be contemplated. However, magnetic anisotropic energy is material-specific, and depends on the material used in the ferromagnetic layers and the state of the interface between the ferromagnetic layers and the other layers. In order to achieve long-term storage of data, the volume of the ferromagnetic layers must be made a predetermined size or greater. For this reason, it is difficult to increase the magnetic anisotropic energy without taking these restrictions into consideration. The ferromagnetic layers are thin-films, for which the volumes are approximately the same as the areas.